A new study in Science has found that the incredible biodiversity of the Amazon rainforest goes back much further than expected, perhaps upending old ideas about how the Amazon basin became arguably the world's most biodiverse ecosystem. According to the study, the origin of rich biodiversity in the Amazon likely goes back more than 20 million years when the Andean mountains were rising.

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"The Andean mountain building profoundly affected the diversity and evolution of the Amazonian biota. It would be difficult to name any major group of Amazonian plants or animals whose fate had not been touched in some way by the formation of the vast Andean mountain chain," William Laurance, a conservation biologist at James Cook University who has spent decades working in the tropics, told mongabay.com. Laurance was not involved with the study.

By comparing biodiversity patterns today with geological and molecular datasets, researchers found that the highest diversity of species were in a region spanning over a million square kilometers which originated with the rising Andes. Given this, the authors believe they have found a strict the connection between the rich diversity Amazon rainforests and the rise of the Andes over 20 million years ago.

The researchers also note that as Andes rose they created a vast wetland appeared in the Amazonian region. This wetland also played a role. Around 10 million years ago when the Amazon River was formed, the wetland dried up, making way for the colonization of new plants and animals.